Method of replacing dispersion medium

ABSTRACT

A method of replacing a first dispersion medium in a starting slurry composed of the first dispersion medium and isophthalic acid crystals with a second dispersion medium. The starting slurry is tangentially fed to a vertically extending cylindrical portion of a cyclone-shaped nozzle disposed at an upper portion of a replacement tank of a dispersion medium replacement apparatus, from a tangential direction of the cylindrical portion. The fed starting slurry moves circularly along an inner wall of the cylindrical portion. The slurry circularly moving is then discharged from an opening which is disposed at a vertically lower end of the cylindrical portion and dispersed in a second dispersion medium which is fed from a lower portion of the replacement tank. The replaced slurry composed of isophthalic acid crystals and the second dispersion medium is mainly discharged from the lower portion of the replacement tank, and the first dispersion medium is mainly withdrawn from the upper portion of the replacement tank.

TECHNICAL FIELD

The present invention relates to a method of replacing a firstdispersion medium in a starting slurry composed of the first dispersionmedium and a isophthalic acid crystal with a second dispersion medium.More specifically, the present invention relates to an efficient methodof replacing a first dispersion medium in a starting slurry composed ofthe first dispersion medium and isophthalic acid crystals, which isproduced by a liquid-phase oxidation reaction or obtained by a treatmentof crude isophthalic acid by a catalytic hydrogenation orrecrystallization and which contains a large amount of impurities, witha second dispersion medium. The method of the present invention issuitably used for producing a high-purity isophthalic acid.

BACKGROUND ART

Isophthalic acid is produced by a liquid-phase oxidation reaction ofm-dialkylbenzenes such as m-xylene. In general, the m-dialkylbenzene issubjected to a liquid-phase oxidation reaction in acetic acid solvent inthe presence of a catalyst such as cobalt and manganese or in theco-presence of the catalyst and an accelerator such as a brominecompound and acetaldehyde to obtain a crude isophthalic acid, and thenthe resultant crude isophthalic acid is purified to obtain the aimedhigh-purity isophthalic acid.

However, since acetic acid is used as a solvent in the above reactionand the reaction product contains impurities such as3-carboxybenzaldehyde (3CBA) and m-toluic acid (m-TOL), a highpurification technique is required to obtain the high-purity isophthalicacid.

There are known various methods for purifying the crude isophthalic acidobtained by the above reaction, such as a method of dissolving the crudeisophthalic acid in acetic acid, water or an acetic acid/water mixedsolvent under high-temperature and high-pressure and then subjecting theresultant solution to catalytic hydrogenation, decarbonylation,oxidation or recrystallization, and a method of subjecting a dispersionpartially dissolving isophthalic acid crystal to high-temperatureimmersion treatment.

In both the production of the crude isophthalic acid by the liquid-phaseoxidation reaction and the purification thereof, the separation of theisophthalic acid crystal from the resultant slurry is finally needed.When the dispersion medium (first dispersion medium) of the reactionproduct solution obtained by the liquid-phase oxidation reaction isacetic acid and a different dispersion medium (second dispersion medium)such as water is used in the purification, it is required to firstseparate the crystals from the reaction product solution and thenre-disperse the separated crystals in the second dispersion medium. Whenthe first dispersion medium in the reaction product solution is the samekind as the second dispersion medium for the subsequent purification, asubstantial part of the impurities such as oxidation intermediate, forexample, 3CBA and m-TOL and coloring substances remain dissolved in thedispersion medium after a high-temperature purifying operation of thereaction product solution of the liquid-phase oxidation reaction or thestarting slurry composed of the first dispersion medium and isophthalicacid crystals. If the reaction product solution of the liquid-phaseoxidation reaction or the starting slurry composed of the firstdispersion medium and isophthalic acid crystals is cooled to about 100°C. while allowing the impurities to be dissolved therein, the impuritiesare included into the isophthalic acid crystals, thereby failing toobtain the aimed high-purity isophthalic acid. Therefore, it isnecessary to conduct the separation at high temperatures under highpressures to separate a high-purity isophthalic acid from the reactionproduct solution obtained by the liquid-phase oxidation reaction, thestarting slurry composed of the first dispersion medium and isophthalicacid crystals or the slurry after the purification treatment.

A centrifugal separation has been most generally used for separating aslurry into crystals and a dispersion medium, which is also extensivelyused in the separation of the reaction product solution obtained by theliquid-phase oxidation reaction or the starting slurry composed of thefirst dispersion medium and isophthalic acid crystals.

In the centrifugal separation, the starting slurry composed of the firstdispersion medium and isophthalic acid crystals is introduced into abasket which is rotating at a high speed to allow the first dispersionmedium to overflow from the upper portion of the basket and allow thecrystals to move downwardly. It has been known that this method involvesseveral problems caused by the limitation in the structures andfunctions due to the operation at high temperatures under highpressures.

Since the rinsing during the centrifugal separation and the rinsing ofthe separated crystals are difficult in this method, the amount of thefirst dispersion medium adhering to the crystals increases. Therefore,the centrifugally separated isophthalic acid crystals are made into aslurry by a further addition of a high-temperature fresh solvent,thereby needing an additional separation into the crystals and thedispersion medium. In addition, the high-speed rotation at hightemperatures under high pressures necessitates a difficult andcomplicated maintenance of the centrifugal separator, to increase theproduction costs.

For example, in the method for producing a high-purity isophthalic aciddisclosed in Patent Document 1, a crude isophthalic acid obtained by aliquid-phase oxidation is catalytically hydrogenated and isophthalicacid is allowed to crystallize to obtain a slurry which is then broughtinto contact with a hot water to exchange the dispersion medium. It isreported that the quality of isophthalic acid which is taken out of thebottom of a tower for replacing dispersion medium is increased bydischarging a part of fine isophthalic acid crystals together with themother liquor of slurry from the top of tower. However, Patent Document1 is completely silent about the uniform dispersion of the isophthalicacid crystals in the tower for replacing dispersion medium.

-   [Patent Document 1] Japanese Patent 3269508

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a method of replacing adispersion medium with another which is capable of uniformly dispersingisophthalic acid crystals contained in a starting slurry composed of theisophthalic acid crystals and a first dispersion medium in thehorizontal direction of an apparatus, and further stably operating thereplacing operation for a long period of time.

The inventors have tried to replace the dispersion medium by bringing aslurry containing isophthalic acid crystals into contact with a hotwater using a known distributor which regulates the flow by throttlingrespective injection orifices. However, this method failed to dispersethe isophthalic acid crystals uniformly in the horizontal direction anddid not allow a stable operation for a long period of time. As a resultof extensive study for solving these problems, the inventors have cometo the use of a centrifugal force to enhance the uniform dispersion ofthe crystals and found a method of replacing a dispersion medium withanother using a cyclone-shaped nozzle having a simple structure and agood dispersion efficiency.

Thus, the present invention relates to a method of replacing adispersion medium with another, comprising the steps of:

feeding a starting slurry composed of a first dispersion medium andisophthalic acid crystals to a cyclone-shaped nozzle disposed at anupper portion of a replacement tank of a dispersion medium replacementapparatus;

contacting the starting slurry discharged from the cyclone-shapednozzles with a second dispersion medium which is fed from a lowerportion of the replacement tank and flows upwardly through thereplacement tank; and

mainly discharging a replaced slurry composed of isophthalic acidcrystal and the second dispersion medium from the lower portion of thereplacement tank and mainly withdrawing the first dispersion medium fromthe upper portion of the replacement tank,

the cyclone-shaped nozzle being composed of a cylindrical portion havinga vertically extending axis and an opening disposed at a verticallylower end, the starting slurry being tangentially fed to the cylindricalportion so as to allow the starting slurry to move circularly along aninner wall of the cylindrical portion, and the starting slurry whichmoves circularly being discharged from the opening, thereby dispersingthe starting slurry in the second dispersion medium.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a perspective view showing an example of a cyclone-shapednozzle, and FIG. 1 b is a sectional view taken along the line V-V inFIG. 1 a.

FIG. 2 a is a perspective view showing another example of acyclone-shaped nozzle, and FIG. 2 b is a sectional view taken along theline V-V in FIG. 2 a.

FIG. 3 a is a perspective view showing still another example of acyclone-shaped nozzle, and FIG. 3 b is a sectional view taken along theline V-V in FIG. 3 a.

FIG. 4 is a schematic view showing a manner of tangentiallydistributively feeding a starting slurry from a ring header into inletsof cyclone-shaped nozzles.

FIG. 5 is a schematic view showing an example of a dispersion mediumreplacement apparatus.

FIG. 6 is a perspective view showing a cyclone-shaped nozzle.

FIG. 7 is a graph showing the distribution of slurry concentration in atank in Reference Example 1.

FIG. 8 is a graph showing the distribution of slurry concentration in atank in Comparative Example 1.

FIG. 9 is a schematic view showing another example of a dispersionmedium replacement apparatus.

FIG. 10 is a graph showing the distribution of slurry concentration in atank in Example 1.

FIG. 11 is a schematic cross-sectional view of cyclone-shaped nozzle forshowing the shape of weir.

BEST MODE FOR CARRYING OUT THE INVENTION

The dispersion medium replacement apparatus used in the presentinvention includes a cyclone-shaped nozzle. Examples of thecyclone-shaped nozzle are shown in FIGS. 1 to 3. However, the structure,shape, etc., of the cyclone-shaped nozzle are not particularly limitedto those shown in these figures as long as it satisfies the followingconditions.

The cyclone-shaped nozzle has a feed portion 21 for feeding a startingslurry and a cylindrical portion (hollow body of revolution) 20connected to the feed portion. The cylindrical portion has a verticallyextending axis (i.e., the cylindrical portion extends in the verticaldirection). Opening 28, 29 is disposed at vertically upper and lowerends, at least at vertically lower end of the cylindrical portion. Thefeed portion 21 is disposed so as to allow the starting slurry to betangentially fed to the cylindrical portion 20. The starting slurry isfed to the cylindrical portion 20 so as to move circularly along aninner wall of the cylindrical portion. The starting slurry which movescircularly is forced to move toward the inner wall of the cylindricalportion by the action of a centrifugal force and the vicinity of theinner wall is filled with the starting slurry which is circularlymoving. The starting slurry flows downwardly while moving circularly,and then discharged from the opening 29 of the cylindrical portion 20,which is formed at the vertically lower end, while keeping the circularmotion. The starting slurry discharged from the cylindrical portion 20is widely distributed and dispersed in the horizontal direction by theaction of the centrifugal force. Since the diameter of the opening 29can be made sufficiently large as compared to the diameter of pores ofthe conventional distributor, the clogging of the opening does not occureven after operating for a long period of time. Weir 22, 34 ispreferably formed at the lower portion of the cylindrical portion 20,and, if necessary, at its upper portion.

As described above, it is important for the cyclone-shaped nozzle usedin the present invention to satisfy the following basic structures (1)to (3):

(1) Including a feed portion for feeding the starting slurry and acylindrical portion having a vertically extending axis which isconnected to the feed portion such that the starting slurry istangentially fed to the cylindrical portion.

(2) An opening for discharging the starting slurry which is circularlymoving is provided at the vertically lower end of the cylindricalportion. Another opening is optionally provided at the vertically upperend of the cylindrical portion.

(3) A weir is provided at the lower portion of the cylindrical portionand at its upper portion, if necessary.

The cylindrical portion (hollow body of revolution) having a verticallyextending axis allows the starting slurry fed thereto to move circularlyalong the inner wall of the cylindrical portion. In the presentinvention, it is important to feed the starting slurry from the nozzleinto the dispersion medium replacement apparatus while keeping thecircular motion of the starting slurry, thereby uniformly distributingand dispersing the starting slurry in the horizontal direction by theaction of the centrifugal force. Therefore, the structure of cylindricalportion is not particularly limited unless the circular motion of thestarting slurry is inhibited. In order to allow the fed starting slurryto move circularly along the inner wall of the cylindrical portion, thefeed portion and the cylindrical portion are preferably connected toeach other so as to tangentially feed the starting slurry to thecylindrical portion.

The opening for allowing the starting slurry which is circularly movingto enter into the dispersion medium replacement apparatus is provided ata vertically lower end of the cyclone-shaped nozzle, as shown in FIGS. 1to 3. In case of preventing the starting slurry from being dispersed orscattered from the upper end of the cylindrical portion, no opening isformed on the upper end (FIG. 3).

To allow the starting slurry to maintain the circular motion, a lowerweir 23 is preferably provided as shown in FIGS. 1 to 3. An upper weir22 may be disposed, if necessary. The weir is formed so as to extendfrom the inner wall of the cylindrical portion 20 toward the center ofthe cylindrical portion horizontally or with a vertically downwardslant. With such a weir, the starting slurry fed is prevented from beingimmediately discharged from the cyclone-shaped nozzle into thedispersion medium replacement apparatus. The shape of the upper weir 22and lower weir 23 is schematically shown in FIGS. 11 a to 11 g with across-sectional view of the cyclone-shaped nozzle.

In the method of replacing a dispersion medium with another according tothe present invention, the starting slurry composed of the firstdispersion medium and isophthalic acid crystals is fed to thecyclone-shaped nozzle disposed at an upper portion of the dispersionmedium replacement apparatus. The second dispersion medium is fed from alower portion of the dispersion medium replacement apparatus. From thelower portion of the dispersion medium replacement apparatus, theresultant replaced slurry composed of isophthalic acid crystals and thesecond dispersion medium is mainly discharged, and the first dispersionmedium is mainly discharged from the upper portion.

As the starting slurry containing the first dispersion medium andisophthalic acid crystals, usable are a reaction product solution of theliquid-phase oxidation and a slurry obtained in the recrystallization ofcrude isophthalic acid.

The reaction product solution of the liquid-phase oxidation is obtainedin the liquid-phase oxidation of m-dialkylbenzene such as m-xylene in anacetic acid solvent in the presence of a catalyst such as cobalt andmanganese or in the co-presence of the catalyst and an accelerator suchas bromine compounds and acetaldehyde. The first dispersion medium ofthe reaction product solution of the liquid-phase oxidation is themother liquor of the oxidation reaction mainly composed of acetic acid.The concentration of isophthalic acid in such starting slurry ispreferably from 10 to 45% by weight, and the concentration of aceticacid in the first dispersion medium is preferably from 70 to 100% byweight. The temperature of the starting slurry to be fed to thedispersion medium replacement apparatus is preferably from 80 to 220° C.

In the purification of the reaction product solution of the liquid-phaseoxidation (starting slurry), either of acetic acid optionally containingwater or water is used as the second dispersion medium. Theconcentration of water in the second dispersion medium is preferablyfrom 50 to 100% by weight. Also, when isophthalic acid crystals arere-dispersed in water, the second dispersion medium is water.

The recrystallization slurry of crude isophthalic acid is obtained inthe step where crude isophthalic acid is dissolved in acetic acid, wateror a mixed solvent thereof at a high temperature under a high pressureand then subjected to a catalytic hydrogenation, decarbonylation,oxidation, or recrystallization. The first dispersion medium in therecrystallization slurry of crude isophthalic acid is acetic acid orwater which dissolves impurities during the recrystallization, and thesecond dispersion medium is water. The concentration of isophthalic acidin the recrystallization slurry is preferably from 10 to 45% by weight.The temperature of the recrystallization slurry to be fed to thedispersion medium replacement apparatus is preferably from 60 to 180° C.

The opening area of the outlet for discharging the starting slurry fromthe cyclone-shaped nozzle, i.e., the area of the opening disposed at thelower end of the cylindrical portion is preferably from 0.03 to 0.8 m².The number of the cyclone-shaped nozzles per horizontal sectional areaof the dispersion medium replacement apparatus is preferably from 0.3 to2/m². The number of the cyclone-shaped nozzles is determined dependingupon the size of the dispersion medium replacement apparatus and theregion (dispersing area) through which the starting slurry dischargedfrom the cyclone-shaped nozzles is horizontally dispersed. The effectivedispersing area of one cyclone-shape nozzle is generally 3 m² or less.Therefore, the number of the cyclone-shaped nozzles per a unit sectionalarea of the dispersion medium replacement apparatus is required to be0.3/m² or more. The number of the cyclone-shaped nozzles per unitsectional area may be made as large as possible. However, if the numberof the cyclone-shaped nozzles is excessively large, the uniform feed ofthe starting slurry to respective cyclone-shaped nozzles becomesdifficult. Therefore, in view of the size of the apparatus industriallyused and the performance of the cyclone-shaped nozzles, the number ofthe cyclone-shaped nozzles exceeding 2/m² is disadvantageous for theindustrial production.

The feed of the starting slurry to two or more cyclone-shaped nozzles ismade by various methods. The most suitable method for the uniformfeeding is to control the flow rate for each cyclone-shaped nozzle, butthis method is costly.

In another method, the concentrated feeding of the starting slurry tosome cyclone-shaped nozzle is prevented by controlling the flow rate byorifices or valves on the basis of the pressure difference between eachpair of cyclone-shaped nozzles which is technically calculated accordingto the design of the cyclone-shaped nozzle. This method may besufficient in a certain size of apparatus. Taking the complexity of theslurry as a fluid and the accuracy of the technical calculation intoaccount, it is difficult to uniformly feed the starting slurry to alarge-scaled apparatus, i.e., a large number of the cyclone-shapednozzles.

In such a large-scaled apparatus having a large number of thecyclone-shaped nozzles, the starting slurry can be fed quite uniformlyinto the cyclone-shaped nozzles by the device as shown in FIG. 4 whichhas a very simple structure, wherein two or more cyclone-shaped nozzlesare connected to a ring header and the starting slurry fed to the ringheader is distributed to respective cyclone-shaped nozzles. The startingslurry is preferably fed to respective cyclone-shaped nozzles along atangential direction of the ring header. If being fed in this manner,the starting slurry is fed to respective cyclone-shaped nozzles whilekeeping the circular motion in the ring header. The starting slurry fedto respective cyclone-shaped nozzles is then discharged into thedispersion medium replacement apparatus while keeping the circularmotion, and distributed and dispersed while moving circularly. With sucha fractal structure of vortex flows, the first dispersion medium in thestarting slurry is effectively replaced with the second dispersionmedium. By the use of the ring header, the starting slurry is uniformlyfed to respective cyclone-shaped nozzles even when the flow rate of thestarting slurry fed to the ring header varies. This effect cannot beachieved by the method of regulating the flow rate by orifices orvalves.

An example of the dispersion medium replacement apparatus is shown inFIG. 9. The starting slurry (isophthalic acid crystals/first dispersionmedium) is fed to a cyclone-shaped nozzle 16 disposed at an upperportion of a replacement tank 12 made of stainless steel, etc. through afeed valve 14 and a feed port 15. In the industrial operation, thereplacement tank 12 preferably has a diameter of from 0.3 to 7 m and aheight of from 1 to 20 m. The diameter of the a cylindrical portion ofthe cyclone-shaped nozzle 16 is preferably from 0.1 to 1 m. The feedingspeed of the starting slurry to be fed to the cyclone-shaped nozzle 16is not particularly limited as long as the starting slurry is dischargedfrom the cyclone-shaped nozzle 16 while keeping the circular motion.When the replacement tank 12 and the cyclone-shaped nozzle 16 have thesizes mentioned above, the feeding speed is preferably from 0.5 to 50t/h.

The second dispersion medium is fed from a feed port 18 disposed in thevicinity of a bottom of the replacement tank 12 through a valvepreferably at a feeding speed of from 0.3 to 40 t/h. The seconddispersion medium fed flows upwardly in the replacement tank 12. Thestarting slurry discharged from the cyclone-shaped nozzle 16 is broughtinto contact with the upward flow of the second dispersion medium, anduniformly distributed and dispersed into the second dispersion medium ina horizontal direction while keeping the circular motion. The dispersedisophthalic acid crystals gravitationally sediment throughout the phaserich in the second dispersion medium, and the replaced slurry composedof isophthalic acid crystals and mainly the second dispersion medium isconcentrated in the lower portion of the replacement tank 12. Thereplaced slurry is discharged from an outlet port 19 using a dischargepump 13. The inner temperature of the replacement tank 12 is preferablykept at from 80 to 180° C.

The first dispersion medium is forced upwardly by the ascending seconddispersion medium and discharged outside of the apparatus from adischarge port 20.

EXAMPLES

The present invention is described in more detail below by referring tothe following examples. However, these examples are only illustrativeand not intended to limit the invention thereto.

Reference Example 1

Using an experimental apparatus as shown in FIG. 5, the state ofdispersion in an experimental replacement tank 1 (diameter: 2 m andheight: 4 m) was observed. A water slurry of sand having a regulatedparticle size (average particle size: 95 μm; concentration of sand: 35%by weight) was used as a starting slurry. The starting slurry wascharged into the experimental replacement tank 1 and circulated to afeed port 5 through an electromagnetic flow meter 4 and a flow controlvalve 3 by using a circulation pump 2 while preventing the sand frombeing deposited on the bottom of the tank.

The circulated starting slurry was fed to the cyclone-shaped nozzle 6,and then discharged and dispersed into the experimental replacement tank1 while keeping the circular motion. The structure of the cyclone-shapednozzle 6 is shown in FIG. 6. A feed portion 11 for feeding the startingslurry was connected to a cylindrical portion 10 so as to tangentiallyfeed the starting slurry. On the vertically upper and lower ends of thecylindrical portion 10 (inner diameter: 0.70 m), an opening 8 (openingdiameter: 0.58 m) and an opening 9 (opening diameter: 0.43 m) wereprovided, respectively.

The slurry was sampled through a sampling nozzle 21 (disposed at aheight of 1.50 m from the bottom of the experimental replacement tank 1)which was disposed through a sampling opening 17 so as to radially movewithin the experimental replacement tank 1, and the concentration ofslurry (concentration of sand in the slurry) was measured. The resultsare shown in the graph of FIG. 7. As seen from FIG. 7, the sand wasuniformly dispersed in the horizontal direction.

The slurry was continuously circulated for 6 h, during which no cloggingof the cyclone-shaped nozzle occurred.

Comparative Example 1

The same procedure as in Reference Example 1 was repeated except forusing a feed nozzle made of an L-shaped tube having a downward openingin place of the cyclone-shaped nozzle, to measure the slurryconcentration distribution within the experimental replacement tank 1.The results are shown in FIG. 8. As seen FIG. 8, the sand was notuniformly dispersed in the horizontal direction.

Comparative Example 2

The starting slurry was circulated in the same manner as in ComparativeExample 1 except for attaching a pigtail disperser to the L-shaped feednozzle used in Comparative Example 1. After 10 min from starting thecirculation, the feed nozzle was clogged.

Example 1

Using an apparatus having the same structure as shown in FIG. 9, thereplacement of the dispersion medium to another was conducted. As thereplacement tank, a closed container made of stainless steel having aninner diameter of 30 cm and a height of 100 cm was used.

The closed container was filled with water maintained at 100° C. Astarting slurry composed of 30% by weight of isophthalic acid and wateras a first dispersion medium was fed at a rate of 770 kg/h to the samecyclone-shaped nozzle as used in Example 1. Water as a second dispersionmedium was fed at a rate of 560 kg/h from a lower portion of thereplacement tank. From the lower portion of the replacement tank, thereplaced slurry composed of isophthalic acid crystals and the seconddispersion medium was mainly discharged. From the upper portion of thereplacement tank, the first dispersion medium was mainly withdrawn. Thereplacement of the dispersion medium to another was continuouslyperformed for one week, during which no troubles such as cloggingoccurred.

The slurry in the replacement tank was sampled using a sampling nozzle21 which was disposed through a sampling opening 17 at horizontallydifferent positions (at a height of 40 m from the bottom of thereplacement tank), to measure the concentration of the slurry(concentration of isophthalic acid crystals in the slurry). As shown inthe graph of FIG. 10, isophthalic acid crystals were uniformly dispersedin the horizontal direction.

INDUSTRIAL APPLICABILITY

In the method of replacing a dispersion medium with another according tothe present invention, a cyclone-shaped nozzle satisfying the specificrequirements is used. By feeding a starting slurry composed of a firstdispersion medium and isophthalic acid crystals through such acyclone-shaped nozzle, isophthalic acid crystals are uniformly dispersedin the horizontal direction, and the replacement operation is stablyconducted for a long period of time.

1. A method of replacing a dispersion medium with another, comprisingthe steps of: feeding a starting slurry which comprises a firstdispersion medium and isophthalic acid crystals to a cyclone-shapednozzle disposed in an upper portion of a replacement tank of adispersion medium replacement apparatus; contacting the starting slurrydischarged from the cyclone-shaped nozzle with a second dispersionmedium which is fed from a lower portion of the replacement tank andflows upwardly through the replacement tank; and mainly discharging areplaced slurry which comprises the isophthalic acid crystals and thesecond dispersion medium from the lower portion of the replacement tankand mainly withdrawing the first dispersion medium from the upperportion of the replacement tank, the cyclone-shaped nozzle comprising ahollow body of revolution having a vertically extending axis and anopening disposed at a vertically lower end, the starting slurry beingtangentially fed to the hollow body of revolution so as to allow thestarting slurry to move circularly along an inner wall of the hollowbody of revolution, and the starting slurry which is circularly movingbeing discharged from the opening, thereby dispersing the startingslurry in the second dispersion medium.
 2. The method according to claim1, wherein an opening area of the opening is from 0.03 to 0.8 m².
 3. Themethod according to claim 1, wherein the number of the cyclone-shapednozzles per sectional area of the replacement tank is from 0.3 to 2/m².4. The method according to claim 1, wherein the starting slurry is fedto two or more cyclone-shaped nozzles connected to a ring header.
 5. Themethod according to claim 1, wherein the starting slurry is a reactionproduct solution of the liquid-phase oxidation of m-dialkylbenzene. 6.The method according to claim 1, wherein the starting slurry is arecrystallization slurry of crude isophthalic acid.
 7. The methodaccording to claim 1, wherein the starting slurry is discharged from theopening while keeping circular motion, such that the discharged slurryis dispersed in the horizontal direction by centrifugal force.
 8. Themethod according to claim 1, wherein the hollow body of revolution has aweir at a lower portion thereof.